Key Engineering Materials Vol. 638

Abstract: Hydroxyapatite (HA) is one of the most common ceramic materials used for bone substitutions or reconstructions [1]. HA synthesis from natural sources is convenient relative to synthetic HA preparation while ensuring a similarity with viable bone tissue in terms of chemical composition and some other properties. One of the most important markers used for hydroxyapatite identification and differentiation from other calcium phosphates is the Ca/P ratio [2]. In order to perform a proper identification, this ratio should be evaluated with high accuracy, which involves a correct determination of the elemental concentrations. This study was made on a series of samples, derived from bovine osseous tissue, thermaly treated at 1000, 1100 and 1200°C. Establishing the influence of sample preparation on the Ca/P ratio assessment from the energy dispersion spectrometry (EDS) coupled with scanning electron microscopy determinations was intended. The samples were prepared by two completely different methods: mechanical fracture (without further preparation) and milling followed by homogenization. Regardless the sample preparation method, the analytical results represents the five measurements average performed on different spots.The EDS results showed that, within the same group, the compositional dissimilarities between the samples treated at different temperatures do not exceed 10% regardless of the sample preparation technique. For the same thermal treatment temperature, slight differences between the elemental chemical compositions of differently prepared samples were observed. The most important effect was a 20% decrease of the average Ca/P ratio for the samples prepared by milling and homogenization in regard to the mechanical fractured ones. Thereby, heat treated bovine bone samples’ milling and further homogenization for performing semi quantitative EDS analysis allows the Ca/P ratio assessment with a better accuracy.

Abstract: Attenuated Total Reflection - Fourier Transform Infrared (ATR-FTIR) spectroscopy is a label-free, non-destructive analytical technique that can be used extensively to study a wide variety of molecules in different conditions. Proteins have very complicated three dimensional structures with multi-level conformations, which are highly correlated with their biological activities. Recently, there is a significant increase of materials based on interaction between proteins and nanoparticles. The aim of this paper is to highlight the understanding of protein interaction with silver nanoparticles (AgNPs) surfaces. Information about the secondary structures of collagen with and without AgNPs was obtained from atomic force microscopy (AFM) measurements.ATR-FTIR spectroscopy was used for monitoring the changes in the secondary structures of collagen upon interaction with AgNPs. Amide I is the most sensitive band for detecting changes in the protein secondary structures. Its characteristic absorption band is located at 1600–1700 cm^-1. Comparing the spectra of collagen with and without AgNPs in this region, information about the different types of secondary structures such as α-helix, β-sheets, turns and random coil can be obtained. The conjugation of AgNPs-collagen occurred mainly through electrostatic interactions. Based on these data, the effects of AgNPs stability and the conformational changes of collagen upon interaction with the AgNPs are discussed.

Abstract: Although the literature describes many studies that attempt to define and interpret the interaction between the metal component and overlying sintered ceramic mass, researchers still have conflicting opinions. It is not yet fully understood the hybrid layer occurrence phenomenon that rises by diffusion at the sintering temperature between the compositional elements of the alloy and the ceramic mass. Also, there isn’t a standardized technology test for the compatibility between the alloy for this technology and a specific plating ceramic mass, from the strength of the bond between the two components at the interface point of view.This paper aims to present the composition, properties and the interaction between the two materials that participates in obtaining metal-ceramic fixed prostheses, and tries to expose a possible method for analysing the bonding strength and compatibility between dental alloys and ceramic masses. However, the mechanical surface contamination by the migration of the chemical elements it is possible, due to the mechanical stresses during cutting and polishing due to the hardness differences between the prosthesis components.Electron microscopy analysis allows the diffusion phenomenon evaluation and of the fact that the elements with reduced concentration within the ceramic have a higher diffusivity (Al as compared with Si), and that metallic elements diffuse in the ceramic mass. The extent of this interdiffusion is probably the degree of adhesion between the two components of the mixed metal-ceramic crown.

Abstract: This work describes the synthesis of composite particles for bone regeneration. The developed method is based on a bio-inspired approach starting from the composition, properties and hierarchical organization of bone extracellular matrix (ECM). The composite material was designed as spherical particles able to ensure interconnected porosity through their assembling inside the bone defect. nanohydroxyapatite was generated in the organic matrix in order to mimic the composition and the organization of the mineral phase in bone tissue. A collagen derivative was used as main natural polymer of the organic matrix of the composite material, in order to mimic the composition of bone ECM. Alginate represents the second organic polymer due to its recognized capacity to easily generate spherical particles in divalent cations solutions. The combination of this polysaccharide with the two previously mentioned components simultaneously responds the architectural and compositional constraints of this approach. The particles were obtained using a modular electrostatic bead generator developed in our laboratory. Briefly, a solution containing the biopolymers was extruded into a mineralisation solution. Spherical particles with diameters of about 500 μm were obtained. They were characterised by scanning electron microscopy, X-ray diffraction, stability in aqueous media. The obtained results confirmed the importance of alginate to generate spherical particles and the potential of such materials to successfully serve the targeted application.

Abstract: This paper presents a comparative study of cellulose acetate membranes, respectively nitrocellulose membranes, synthesized under the same conditions for the retention of proteins from aqueous solutions. It has also been studied the hydrodynamic behavior of the membranes, measuring water, respectively ethanol flow rates, and the retention of proteins. The membranes have been characterized by scanning electron microscopy in order to study the morphological differences.

Abstract: In the present study, four different types of the commercial dental implants used as support for total/partial dental prosthesis have been investigated. Pure Ti and Ti6Al4V alloy, provided by four different manufactures, were chosen because these were the most used in dentistry market. The corrosion resistance was evaluated by using linear polarization technique, after recording the open circuit curves in Fusayama Meyer artificial saliva for 240 minutes. The corrosion tests in artificial saliva with pH 5.2 have shown that pure Ti exhibited a better behavior than the Ti alloy. This result can be explained by a higher stability of the passive thin layer of titanium oxide than the complex oxide layer formed on the Ti alloy surface.

Abstract: This work presents the synthesis and characterization of natural-synthetic hydrogels based on gelatin (Gel) and polyvinylpyrrolidone (PVP), with potential for skin grafts applications. The natural component, Gel insures the biocompatibility and biodegradability of the bicomponent system [1], while the synthetic counterpart, PVP, is a physiologic inert component, extensively used in medicine due to its water affinity and due to its capacity of confer elasticity to films and membranes with potential applications in skin grafts [2]. The obtained hydrogels were subjected to morpho-structural analysis and rheological and mechanical tests (traction). The water affinity of the systems was estimated and their capacity to generate porous substrates through freeze-drying was evaluated.

Abstract: TiSiN thin films were deposited on NiCr dental alloy in order to enhance the corrosion resistance in artificial saliva with and without fluoride content. The TiSiN films were prepared using reactive cathodic arc method at two different substrate bias voltages (-50 V and-200 V). For the corrosion evaluation, artificial saliva with pH=5.2 was chosen, because this is a critical value for mineral dissolution of dental tissue which can affect the dental alloys. A content of 0.1 % NaF was added to the artificial saliva to simulate the effect of fluoride based hygiene products. The TiSiN coated NiCr alloys exhibited a higher corrosion resistance than the NiCr substrate, irrespective of the testing environment. The best corrosion resistance was found for the TiSiN deposited at-200 V.

Abstract: This work describes the investigation of the properties of hydrogels based on methacrylamide-modified gelatin (GelMA) and polyvinylpyrrolidone (PVP) with potential applications in wound treatment. While the semi-natural polymer insures the biocompatibility and biodegradability of the synthesized materials, the synthetic polymer was selected due to its water affinity and interesting mechanical properties. The efficiency of the polymerization process and the stability of the PVP within the semi interpenetrated polymer network (semiIPN) were verified through gel fraction study. The water affinity, tensile strength and rheological properties of the hydrogels were also investigated.